Identification of genes that are essential to restrict genome duplication to once per cell division

RAD51 restricts DNA over-replication from re-activated origins

Eukaryotic cells rely on several mechanisms to ensure that the genome is duplicated precisely once in each cell division cycle, preventing DNA over-replication and genomic instability. Most of these mechanisms limit the activity of origin licensing proteins to prevent the reactivation of origins that have already been used. Here, we have investigated whether additional controls restrict the extension of re-replicated DNA in the event of origin re-activation. In a genetic screening in cells forced to re-activate origins, we found that re-replication is limited by RAD51 and enhanced by FBH1, a RAD51 antagonist. In the presence of chromatin-bound RAD51, forks stemming from re-fired origins are slowed down, leading to frequent events of fork reversal. Eventual re-initiation of DNA synthesis mediated by PRIMPOL creates ssDNA gaps that facilitate the partial elimination of re-duplicated DNA by MRE11 exonuclease. In the absence of RAD51, these controls are abrogated and re-replication forks progress much longer than in normal conditions. Our study uncovers a safeguard mechanism to protect genome stability in the event of origin reactivation.

Chromosome hyperploidy induced by chronic hepatitis B virus infection and its targeted therapeutic strategy

Chronic hepatitis B virus (HBV) infection induces chromosomal hyperploidy (including aneuploidy and polyploidy) and chromosomal instability in hepatocytes, which is one of the main causes of primary hepatocellular carcinoma (HCC). Although hepatocytes can regulate polyploidization of chromosomes under normal conditions, it is difficult to regulate hyperploidization caused by HBV infection and thus carcinogenesis. Studies have shown that HBV can cause dysregulation of many signal pathways such as PLK1/PRC1, and induce chromosome hyperploidy and malignant transformation of hepatocytes. Herein we review the mechanism of HBV infection-induced chromosomal hyperploidy of hepatocytes to cuase hepatocarcinogenesis and the advances in research of drugs targeting chromosomal hyperploidy.

Adaptive exchange sustains cullin-RING ubiquitin ligase networks and proper licensing of DNA replication

Cop9 signalosome (CSN) regulates the function of cullin-RING E3 ubiquitin ligases (CRLs) by deconjugating the ubiquitin-like protein NEDD8 from the cullin subunit. To understand the physiological impact of CSN function on the CRL network and cell proliferation, we combined quantitative mass spectrometry and genome-wide CRISPR interference (CRISPRi) and CRISPR activation (CRISPRa) screens to identify factors that modulate cell viability upon inhibition of CSN by the small molecule CSN5i-3. CRL components and regulators strongly modulated the antiproliferative effects of CSN5i-3, and in addition we found two pathways involved in genome integrity, SCF^FBXO5-APC/C-GMNN and CUL4^DTL-SETD8, that contribute substantially to the toxicity of CSN inhibition. Our data highlight the importance of CSN-mediated NEDD8 deconjugation and adaptive exchange of CRL substrate receptors in sustaining CRL function and suggest approaches for leveraging CSN inhibition for the treatment of cancer.

A Temporary Pause in the Replication Licensing Restriction Leads to Rereplication during Early Human Cell Differentiation

Gene amplifications in amphibians and flies are known to occur during development and have been well characterized, unlike in mammalian cells, where they are predominantly investigated as an attribute of tumors. Recently, we first described gene amplifications in human and mouse neural stem cells, myoblasts, and mesenchymal stem cells during differentiation. The mechanism leading to gene amplifications in amphibians and flies depends on endocycles and multiple origin-firings. So far, there is no knowledge about a comparable mechanism in normal human cells. Here, we describe rereplication during the early myotube differentiation of human skeletal myoblast cells, using fiber combing and pulse-treatment with EdU (5′-Ethynyl-2′-deoxyuridine)/CldU (5-Chlor-2′-deoxyuridine) and IdU (5-Iodo-2′-deoxyuridine)/CldU. We found rereplication during a restricted time window between 2 h and 8 h after differentiation induction. Rereplication was detected in cells simultaneously with the amplification of the MDM2 gene. Our findings support rereplication as a mechanism enabling gene amplification in normal human cells.

Extracting functional insights from loss-of-function screens using deep link prediction

We present deep link prediction (DLP), a method for the interpretation of loss-of-function screens. Our approach uses representation-based link prediction to reprioritize phenotypic readouts by integrating screening experiments with gene-gene interaction networks. We validate on 2 different loss-of-function technologies, RNAi and CRISPR, using datasets obtained from DepMap. Extensive benchmarking shows that DLP-DeepWalk outperforms other methods in recovering cell-specific dependencies, achieving an average precision well above 90% across 7 different cancer types and on both RNAi and CRISPR data. We show that the genes ranked highest by DLP-DeepWalk are appreciably more enriched in drug targets compared to the ranking based on original screening scores. Interestingly, this enrichment is more pronounced on RNAi data compared to CRISPR data, consistent with the greater inherent noise of RNAi screens. Finally, we demonstrate how DLP-DeepWalk can infer the molecular mechanism through which putative targets trigger cell line mortality.

Etoposide-induced DNA damage is increased in p53 mutants: identification of ATR and other genes that influence effects of p53 mutations on Top2-induced cytotoxicity

The functional status of the tumor suppressor p53 is a critical component in determining the sensitivity of cancer cells to many chemotherapeutic agents. DNA topoisomerase II (Top2) plays essential roles in DNA metabolism and is the target of FDA approved chemotherapeutic agents. Topoisomerase targeting drugs convert the enzyme into a DNA damaging agent and p53 influences cellular responses to these agents. We assessed the impact of the loss of p53 function on the formation of DNA damage induced by the Top2 poison etoposide. Using human HCT116 cells, we found resistance to etoposide in cell growth assays upon the functional loss of p53. Nonetheless, cells lacking fully functional p53 were etoposide hypersensitive in clonogenic survival assays. This complex role of p53 led us to directly examine the effects of p53 status on topoisomerase-induced DNA damage. A deficiency in functional p53 resulted in elevated levels of the Top2 covalent complexes (Top2cc) in multiple cell lines. Employing genome-wide siRNA screens, we identified a set of genes for which reduced expression resulted in enhanced synthetic lethality upon etoposide treatment of p53 defective cells. We focused on one hit from this screen, ATR, and showed that decreased expression sensitized the p53-defective cells to etoposide in all assays and generated elevated levels of Top2cc in both p53 proficient and deficient cells. Our findings suggest that a combination of etoposide treatment with functional inactivation of DNA repair in p53 defective cells could be used to enhance the therapeutic efficacy of Top2 targeting agents.

Combined Inhibition of p38MAPK and PIKfyve Synergistically Disrupts Autophagy to Selectively Target Cancer Cells

In nutrient-poor conditions, autophagy buffers metabolic stress and counteracts the effects of chemotherapy and radiation on cancer cells, which depend on autophagy for survival. However, clinical trials targeting autophagy have failed to produce successful anticancer treatments using currently available inhibitors. Recent studies have shown that PIKfyve kinase inhibitors disrupt lysosome function in autophagy and can selectively kill certain cancer cells. Analysis of biochemical changes caused by PIKfyve inhibition revealed that resistant cells contain significantly higher levels of cellular p38MAPK protein and phosphorylation. Expression of the lysosomal protein, lysosomal-associated membrane protein 2, carrying phosphomimetic mutations of the p38MAPK phosphorylation sites prevented all effects caused by PIKfyve inhibition-induced lysosome dysfunction. Thus, the activation of p38MAPK in response to PIKfyve inhibition revealed a novel compensatory role in maintaining lysosome function in autophagy. The functional cooperation between the cellular PIKfyve and p38MAPK pathways in regulating lysosome homeostasis was especially important in cancer cells. Combined inhibition of PIKfyve and p38MAPK activities synergistically blocked autophagy-mediated protein degradation, prevented cathepsin maturation, and markedly reduced the viability of multiple cancer cell types without affecting the viability of normal cells. Furthermore, combined PIKfyve and p38MAPK inhibitors synergistically reduced tumor growth in mice bearing xenografts of human colorectal adenocarcinoma, suggesting a novel way to target cancer cells by prolonged inhibition of autophagy using lower drug concentrations. SIGNIFICANCE: This study demonstrates that PIKfyve and p38MAPK cooperate to regulate lysosome homeostasis and their combined inhibition synergistically blocks autophagy to reduce cancer cell viability in vitro and in vivo.

Cell cycle arrest and apoptosis are not dependent on p53 prior to p53-dependent embryonic stem cell differentiation

Previous efforts to determine whether or not the transcription factor and tumor suppressor protein p53 is required for DNA damage-induced apoptosis in pluripotent embryonic stem cells (ESCs) produced contradictory conclusions. To resolve this issue, p53+/+ and p53-/- ESCs derived by two different methods were used to quantify time-dependent changes in nuclear DNA content; annexin-V binding; cell permeabilization; and protein expression, modification, and localization. The results revealed that doxorubicin (Adriamycin [ADR]) concentrations 10 to 40 times less than commonly used in previous studies induced the DNA damage-dependent G2-checkpoint and completed apoptosis within the same time frame, regardless of the presence or absence of p53, p21, and PUMA. Increased ADR concentrations delayed initiation of apoptosis in p53-/- ESCs, but the rates of apoptosis remained equivalent. Similar results were obtained by inducing apoptosis with either staurosporine inhibition of kinase activities or WX8 disruption of lysosome homeostasis. Differentiation of ESCs by LIF deprivation revealed p53-dependent formation of haploid cells, increased genomic stability, and suppression of the G2-checkpoint. Minimal induction of DNA damage now resulted in p53-facilitated apoptosis, but regulation of pluripotent gene expression remained p53-independent. Primary embryonic fibroblasts underwent p53-dependent total cell cycle arrest (a prelude to cell senescence), and p53-independent apoptosis occurred in the presence of 10-fold higher levels of ADR, consistent with previous studies. Taken together, these results reveal that the multiple roles of p53 in cell cycle regulation and apoptosis are first acquired during pluripotent stem cell differentiation.

BRCA1 and S phase DNA repair pathways restrict LINE-1 retrotransposition in human cells

Long interspersed element-1 (LINE-1 or L1) is the only autonomous retrotransposon active in human cells. Different host factors have been shown to influence L1 mobility however, systematic analyses of these factors are limited. Here, we developed a high-throughput microscopy-based retrotransposition assay that identified the Double-Stranded Break (DSB) repair and Fanconi Anemia factors active in the S/G2 phase as potent inhibitors and regulators of L1 activity. In particular BRCA1, an E3 ubiquitin ligase with a key role in several DNA repair pathways, directly affects L1 retrotransposition frequency and structure and also plays a distinct role in controlling L1 ORF2 protein translation through L1 mRNA binding. These results suggest the existence of a “battleground” at the DNA replication fork between HR factors and L1 retrotransposons, and revealing a potential role for L1 in the genotypic evolution of tumors characterized by BRCA1 and HR repair deficiencies.

A Cyclin A-Myb-MuvB-Aurora B network regulates the choice between mitotic cycles and polyploid endoreplication cycles

Endoreplication is a cell cycle variant that entails cell growth and periodic genome duplication without cell division, and results in large, polyploid cells. Cells switch from mitotic cycles to endoreplication cycles during development, and also in response to conditional stimuli during wound healing, regeneration, aging, and cancer. In this study, we use integrated approaches in Drosophila to determine how mitotic cycles are remodeled into endoreplication cycles, and how similar this remodeling is between induced and developmental endoreplicating cells (iECs and devECs). Our evidence suggests that Cyclin A / CDK directly activates the Myb-MuvB (MMB) complex to induce transcription of a battery of genes required for mitosis, and that repression of CDK activity dampens this MMB mitotic transcriptome to promote endoreplication in both iECs and devECs. iECs and devECs differed, however, in that devECs had reduced expression of E2F1-dependent genes that function in S phase, whereas repression of the MMB transcriptome in iECs was sufficient to induce endoreplication without a reduction in S phase gene expression. Among the MMB regulated genes, knockdown of AurB protein and other subunits of the chromosomal passenger complex (CPC) induced endoreplication, as did knockdown of CPC-regulated cytokinetic, but not kinetochore, proteins. Together, our results indicate that the status of a CycA-Myb-MuvB-AurB network determines the decision to commit to mitosis or switch to endoreplication in both iECs and devECs, and suggest that regulation of different steps of this network may explain the known diversity of polyploid cycle types in development and disease.

The broken cycle: E2F dysfunction in cancer

The cyclin-dependent kinase (CDK)-RB-E2F axis forms the core transcriptional machinery driving cell cycle progression, dictating the timing and fidelity of genome replication and ensuring genetic material is accurately passed through each cell division cycle. The ultimate effectors of this axis are members of a family of eight distinct E2F genes encoding transcriptional activators and repressors. E2F transcriptional activity is tightly regulated throughout the cell cycle via transcriptional and translational regulation, post-translational modifications, protein degradation, binding to cofactors and subcellular localization. Alterations in one or more key components of this axis (CDKs, cyclins, CDK inhibitors and the RB family of proteins) occur in virtually all cancers and result in heightened oncogenic E2F activity, leading to uncontrolled proliferation. In this Review, we discuss the activities of E2F proteins with an emphasis on the newest atypical E2F family members, the specific and redundant functions of E2F proteins, how misexpression of E2F transcriptional targets promotes cancer and both current and developing therapeutic strategies being used to target this oncogenic pathway.

Flow Cytometry Analysis of Fungal Ploidy

Ploidy, the number of sets of homologous chromosomes in a cell, can alter cellular physiology, gene regulation, and the spectrum of acquired mutations. Advances in single-cell flow cytometry have greatly improved the understanding of how genome size contributes to diverse biological processes including speciation, adaptation, pathogenesis, and tumorigenesis. For example, fungal pathogens can undergo whole genome duplications during infection of the human host and during acquisition of antifungal drug resistance. Quantification of ploidy is dramatically affected by the nucleic acid staining technique and the flow cytometry analysis of single cells. Ploidy in fungi is also impacted by samples that are heterogeneous for both ploidy and morphology, and control strains with known ploidy must be included in every flow cytometry experiment. To detect ploidy changes within fungal strains, the following protocol was developed to accurately and dependably interrogate single-cell ploidy. © 2018 by John Wiley & Sons, Inc.

Machine learning models to predict the progression from early to late stages of papillary renal cell carcinoma

Papillary Renal Cell Carcinoma (PRCC) is a heterogeneous disease with variations in disease progression and clinical outcomes. The advent of next generation sequencing techniques (NGS) has generated data from patients that can be analysed to develop a predictive model. In this study, we have adopted a machine learning approach to identify biomarkers and build classifiers to discriminate between early and late stages of PRCC from gene expression profiles. A machine learning pipeline incorporating different feature selection algorithms and classification models is developed to analyse RNA sequencing dataset (RNASeq). Further, to get a reliable feature set, we extracted features from different partitions of the training dataset and aggregated them into feature sets for classification. We evaluated the performance of different algorithms on the basis of 10-fold cross validation and independent test dataset. 10-fold cross validation was also performed on a microarray dataset of PRCC. A random forest based feature selection (varSelRF) yielded minimum number of features (104) and a best performance with area under Precision Recall curve (PR-AUC) of 0.804, MCC (Matthews Correlation Coefficient) of 0.711 and accuracy of 88% with Shrunken Centroid classifier on a test dataset. We identified 80 genes that are consistently altered between stages by different feature selection algorithms. The extracted features are related to cellular components - centromere, kinetochore and spindle, and biological process mitotic cell cycle. These observations reveal potential mechanisms for an increase in chromosome instability in the late stage of PRCC. Our study demonstrates that the gene expression profiles can be used to classify stages of PRCC.

Ploidy Variation in Fungi: Polyploidy, Aneuploidy, and Genome Evolution

The ability of an organism to replicate and segregate its genome with high fidelity is vital to its survival and for the production of future generations. Errors in either of these steps (replication or segregation) can lead to a change in ploidy or chromosome number. While these drastic genome changes can be detrimental to the organism, resulting in decreased fitness, they can also provide increased fitness during periods of stress. A change in ploidy or chromosome number can fundamentally change how a cell senses and responds to its environment. Here, we discuss current ideas in fungal biology that illuminate how eukaryotic genome size variation can impact the organism at a cellular and evolutionary level. One of the most fascinating observations from the past 2 decades of research is that some fungi have evolved the ability to tolerate large genome size changes and generate vast genomic heterogeneity without undergoing canonical meiosis.

PRC1: Linking Cytokinesis, Chromosomal Instability, and Cancer Evolution

Cytokinesis is the final event of the cell cycle dividing one cell into two daughter cells. The protein regulator of cytokinesis (PRC)1 is essential for cytokinesis and normal cell cleavage. Deregulation of PRC1 causes cytokinesis defects that promote chromosomal instability (CIN) and thus tumor heterogeneity and cancer evolution. Consistently, abnormal PRC1 expression correlates with poor patient outcome in various malignancies, which may be caused by PRC1-mediated CIN and aneuploidy. Here, we review the physiological functions of PRC1 in cell cycle regulation and its contribution to tumorigenesis and intratumoral heterogeneity. We discuss targeting PRC1 within the complementary approaches of either normalizing CIN in aneuploid cancers or creating chromosomal chaos in genomically stable cancers to induce apoptosis.

Geminin deficiency enhances survival in a murine medulloblastoma model by inducing apoptosis of preneoplastic granule neuron precursors

Medulloblastoma is the most common malignant brain cancer of childhood. Further understanding of tumorigenic mechanisms may define new therapeutic targets. Geminin maintains genome fidelity by controlling re-initiation of DNA replication within a cell cycle. In some contexts, Geminin inhibition induces cancer-selective cell cycle arrest and apoptosis and/or sensitizes cancer cells to Topoisomerase IIα inhibitors such as etoposide, which is used in combination chemotherapies for medulloblastoma. However, Geminin's potential role in medulloblastoma tumorigenesis remained undefined. Here, we found that Geminin is highly expressed in human and mouse medulloblastomas and in murine granule neuron precursor (GNP) cells during cerebellar development. Conditional Geminin loss significantly enhanced survival in the SmoA1 mouse medulloblastoma model. Geminin loss in this model also reduced numbers of preneoplastic GNPs persisting at one postnatal month, while at two postnatal weeks these cells exhibited an elevated DNA damage response and apoptosis. Geminin knockdown likewise impaired human medulloblastoma cell growth, activating G2 checkpoint and DNA damage response pathways, triggering spontaneous apoptosis, and enhancing G2 accumulation of cells in response to etoposide treatment. Together, these data suggest preneoplastic and cancer cell-selective roles for Geminin in medulloblastoma, and suggest that targeting Geminin may impair tumor growth and enhance responsiveness to Topoisomerase IIα-directed chemotherapies.

Non-Canonical Replication Initiation: You're Fired!

The division of prokaryotic and eukaryotic cells produces two cells that inherit a perfect copy of the genetic material originally derived from the mother cell. The initiation of canonical DNA replication must be coordinated to the cell cycle to ensure the accuracy of genome duplication. Controlled replication initiation depends on a complex interplay of cis-acting DNA sequences, the so-called origins of replication (ori), with trans-acting factors involved in the onset of DNA synthesis. The interplay of cis-acting elements and trans-acting factors ensures that cells initiate replication at sequence-specific sites only once, and in a timely order, to avoid chromosomal endoreplication. However, chromosome breakage and excessive RNA:DNA hybrid formation can cause break-induced (BIR) or transcription-initiated replication (TIR), respectively. These non-canonical replication events are expected to affect eukaryotic genome function and maintenance, and could be important for genome evolution and disease development. In this review, we describe the difference between canonical and non-canonical DNA replication, and focus on mechanistic differences and common features between BIR and TIR. Finally, we discuss open issues on the factors and molecular mechanisms involved in TIR.

Links between DNA Replication, Stem Cells and Cancer. Genes (Basel). 2017;8. [PMID: 28125050 PMCID: PMC5333035 DOI: 10.3390/genes8020045]

Cancers can be categorized into two groups: those whose frequency increases with age, and those resulting from errors during mammalian development. The first group is linked to DNA replication through the accumulation of genetic mutations that occur during proliferation of developmentally acquired stem cells that give rise to and maintain tissues and organs. These mutations, which result from DNA replication errors as well as environmental insults, fall into two categories; cancer driver mutations that initiate carcinogenesis and genome destabilizing mutations that promote aneuploidy through excess genome duplication and chromatid missegregation. Increased genome instability results in accelerated clonal evolution leading to the appearance of more aggressive clones with increased drug resistance. The second group of cancers, termed germ cell neoplasia, results from the mislocation of pluripotent stem cells during early development. During normal development, pluripotent stem cells that originate in early embryos give rise to all of the cell lineages in the embryo and adult, but when they mislocate to ectopic sites, they produce tumors. Remarkably, pluripotent stem cells, like many cancer cells, depend on the Geminin protein to prevent excess DNA replication from triggering DNA damage-dependent apoptosis. This link between the control of DNA replication during early development and germ cell neoplasia reveals Geminin as a potential chemotherapeutic target in the eradication of cancer progenitor cells.

The pathological consequences of impaired genome integrity in humans; disorders of the DNA replication machinery

Accurate and efficient replication of the human genome occurs in the context of an array of constitutional barriers, including regional topological constraints imposed by chromatin architecture and processes such as transcription, catenation of the helical polymer and spontaneously generated DNA lesions, including base modifications and strand breaks. DNA replication is fundamentally important for tissue development and homeostasis; differentiation programmes are intimately linked with stem cell division. Unsurprisingly, impairments of the DNA replication machinery can have catastrophic consequences for genome stability and cell division. Functional impacts on DNA replication and genome stability have long been known to play roles in malignant transformation through a variety of complex mechanisms, and significant further insights have been gained from studying model organisms in this context. Congenital hypomorphic defects in components of the DNA replication machinery have been and continue to be identified in humans. These disorders present with a wide range of clinical features. Indeed, in some instances, different mutations in the same gene underlie different clinical presentations. Understanding the origin and molecular basis of these features opens a window onto the range of developmental impacts of suboptimal DNA replication and genome instability in humans. Here, I will briefly overview the basic steps involved in DNA replication and the key concepts that have emerged from this area of research, before switching emphasis to the pathological consequences of defects within the DNA replication network; the human disorders. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Validation of Synthetic CRISPR Reagents as a Tool for Arrayed Functional Genomic Screening

To date, lentiviral-based CRISPR-Cas9 screens have largely been conducted in pooled format. However, numerous assays are not amenable to pooled approaches, and lentiviral screening in arrayed format presents many challenges. We sought to examine synthetic CRISPR reagents in the context of arrayed screening. Experiments were performed using aberrant DNA replication as an assay. Using synthetic CRISPR RNAs targeting the known control gene GMNN in HCT-116 cells stably expressing Cas9, we observed statistically significant phenotype among the majority of transfected cells within 72 hours. Additional studies revealed near complete loss of GMNN protein and editing of GMNN DNA. We next conducted a screen of synthetic CRISPR RNAs directed against 640 ubiquitin-related genes. Screening identified known and novel DNA replication regulators that were also supported by siRNA gene knockdown. Notably, CRISPR screening identified more statistically significant hits than corresponding siRNA screens run in parallel. These results highlight the possibility of using synthetic CRISPR reagents as an arrayed screening tool.

Geminin Is Essential for Pluripotent Cell Viability During Teratoma Formation, but Not for Differentiated Cell Viability During Teratoma Expansion

Pluripotent embryonic stem cells (ESCs) are unusual in that geminin has been reported to be essential either to prevent differentiation by maintaining expression of pluripotency genes or to prevent DNA rereplication-dependent apoptosis. To distinguish between these two incompatible hypotheses, immune-compromised mice were inoculated subcutaneously with ESCs harboring conditional Gmnn alleles alone or together with a tamoxifen-dependent Cre recombinase gene. Mice were then injected with tamoxifen at various times during which the ESCs proliferated and differentiated into a teratoma. For comparison, the same ESCs were cultured in vitro in the presence of monohydroxytamoxifen. The results revealed that geminin is a haplosufficient gene that is essential for ESC viability before they differentiate into a teratoma, but once a teratoma is established, the differentiated cells can continue to proliferate in the absence of Gmnn alleles, geminin protein, and pluripotent stem cells. Thus, differentiated cells did not require geminin for efficient proliferation within the context of a solid tissue, although they did when teratoma cells were cultured in vitro. These results provide proof-of-principle that preventing geminin function could prevent malignancy in tumors derived from pluripotent cells by selectively eliminating the progenitor cells with little harm to normal cells.

Geminin a multi task protein involved in cancer pathophysiology and developmental process: A review

DNA replicates in a timely manner with each cell division. Multiple proteins and factors are involved in the initiation of DNA replication including a dynamic interaction between Cdc10-dependent transcript (Cdt1) and Geminin (GMNN). A conformational change between GMNN-Cdt1 heterotrimer and heterohexamer complex is responsible for licensing or inhibition of the DNA replication. This molecular switch ensures a faithful DNA replication during each S phase of cell cycle. GMNN inhibits Cdt1-mediated minichromosome maintenance helicases (MCM) loading onto the chromatin-bound origin recognition complex (ORC) which results in the inhibition of pre-replication complex assembly. GMNN modulates DNA replication by direct binding to Cdt1, and thereby alters its stability and activity. GMNN is involved in various stages of development such as pre-implantation, germ layer formation, cell commitment and specification, maintenance of genome integrity at mid blastula transition, epithelial to mesenchymal transition during gastrulation, neural development, organogenesis and axis patterning. GMNN interacts with different proteins resulting in enhanced hematopoietic stem cell activity thereby activating the development-associated genes' transcription. GMNN expression is also associated with cancer pathophysiology and development. In this review we discussed the structure and function of GMNN in detail. Inhibitors of GMNN and their role in DNA replication, repair, cell cycle and apoptosis are reviewed. Further, we also discussed the role of GMNN in virus infected host cells.